S286: TARGETING CONDITIONING-ELICITED NON-TRANSFERRIN-BOUND IRON BY TMPRSS6 SILENCING IMPROVES BONE MARROW TRANSPLANT OUTCOME
Authors: Ada Antypiuk, Alberto Martinez, Ute Schaeper, Uwe Platzbecker, Francesca Vinchi
Journal: HemaSphere (2023)

Background: Hematopoietic stem cell transplantation (HSCT) remains the only fully curative therapy for diseases such as b-thalassemia, sickle cell disease, MDS and AML and a relevant procedure for gene therapy. Tissue iron overload and, recently, non-transferrin bound iron (NTBI) have emerged as adverse prognostic factors for post-transplant survival. Thus, it has remained elusive whether NTBI or iron stores is the true mediator of peri-transplant iron toxicities. Aims: These observations highlight the need for elucidation of the underlying pathophysiological mechanisms mediating the unfavorable prognostic effects of excess iron in transplanted patients. In this study we monitored peri-transplant NTBI formation and its impact on bone marrow transplant (BMT) outcome in absence of pre-existing tissue iron-overload. Methods: To this purpose we treated CD45.2+ wild-type mice with a combination of busulfan and fludarabine as preparatory conditioning for BMT and analyzed systemic iron parameters and engraftment of CD45.1+ transplanted BM cells. To evaluate NTBI role, a GalNAc conjugated siRNA capable of increasing hepcidin level by silencing TMPRSS6 was administered pre-conditioning in recipient wild-type mice to achieve iron restriction. Results: Chemotherapy conditioning in wild-type mice resulted in elevated serum iron and transferrin (Tf) saturation and elicited NTBI formation at the end of chemotherapy administration. Tf saturation and NTBI levels increased proportionally with conditioning intensity. Pre-conditioning TMPRSS6 silencing - by increasing hepcidin - reduced the peri-transplant elevation of Tf saturation and limited the appearance of NTBI. These results prove that NTBI formation is induced by conditioning chemotherapy independently of the presence of pre-existing iron overload. Importantly, pre-conditioning TMPRSS6 silencing in recipient CD45.2+ wild-type mice increased BM and spleen engraftment of CD45.1+ donor cells and resulted in more elevated blood chimerism. Multilineage engraftment in BM, spleen and peripheral blood was superior in iron-restricted recipient mice compared to controls. These findings demonstrate that conditioning-elicited NTBI is sufficient –per se– to negatively impact donor cell engraftment after BMT and that reducing peri-transplant NTBI formation improves BMT outcome by increasing engraftment efficiency. Finally, donor chimerism of HSCs was higher and inflammatory cytokine production by BM immune cells was lower in iron-restricted versus control transplanted mice. Overall, these data indicate that iron restriction improves donor HSC engraftment and decreases inflammation in the recipient BM, likely resulting in more efficient reconstitution of the HSC pool and improved multilineage engraftment. Summary/Conclusion: Our findings prove that conditioning-elicited NTBI is a critical mediator of peri-transplant toxicity and adversely impacts transplant outcome by reducing HSPC engraftment and heightening inflammation. Lastly, our results demonstrate that the peri-transplant application of novel iron restriction strategies aimed at reducing conditioning-induced NTBI positively affects BMT outcome, with potential benefit for patients undergoing BMT or gene therapy. Keywords: Hematopoietic cell transplantation, Iron